Method of detecting flaws in articles



United States Patent METHOD OF DETECTING FLAWS 1N ARTICLES William Claud Lockwood, East Kiihride, Lanarkshire,

Scotland, assignor to Rolls-Royce Limited, Derby, England, a company of Great Britain lilo Drawing. Filed Jan. 8, 1969, Ser. No. 1,172 Claims priority, application Great Britain Feb. 18, 1959 12 Claims. (Cl. 25071) This invention concerns an improved method of detecting flaws in articles.

According to the present invention there is provided a method of detecting flaws (e.g. cracks) in a liquidimpermeable surface of a body comprising applying to said surface a liquid penetrant so that the latter penetrates into the said flaws; employing finely divided particulate material to remove the penetrant completely from the unfiawed parts of said surface While leaving the penetrant in said flaws and while leaving said surface sub stantially unimpaired in quality and dimensions; and

1riendering visible the penetrant which has been left in the aws.-

The finely divided particulate material may comprise powdered fruit stones (e.g. powdered plum stones) or powdered nut shells (e.g. powdered walnut shells).

The penetrant may be removed from the unilawed parts of the surface by blowing the particulate material onto said surface.

Alternatively, the penetrant may be removed from the unliawed parts of said surface by tumbling the body in a water-saturated aggregate comprising finely-divided particulate material.

The said aggregate may comprise tumbling chips. Thus the aggregate may comprise substantially 50% by weight of finely divided plum stones and 50% by weight of granite or aloxite tumbling chips.

Preferably the penetrant is rendered visible by applying to said surface a powder which is adapted to absorb or adsorb the penetrant.

The penetrant may be'a fluorescent substance or may be coloured with a fluorescent dye, the penetrant left in the flaws being detected by viewing said surface under ultra-violet light.

Alternatively the penetrant may be non-fluorescent and have a colour which is readily distinguishable from that of the surface of said body. Thus the penetrant may con tain a non-luorescent dye (e.g. a simple red dye).

The removal of the surplus penetrant may be partially effected by washing said surface prior to the treatment with the finely divided particulate material.

Any finely divided particulate material adhering to the said surface after the said treatment may, if desired, be removed prior to the rendering visible of the penetrant which has been left in the fiaws.

The invention will now be described, merely by way of example, with reference to its application to the detection of flaws in a compressor rotor blade.

If the blade has any surface contamination (e.g. grease i or till) this is first removed, e.g. by employing trichlorethylene vapour at 87 to 120 C.

The blade is then submerged in a fluorescent liquid penetrant which is adapted to penetrate into the cracks and other flaws in the surface of the blade. If the blade has been treated with the hot trichlorethylene vapour it will of course have become heated itself. It may nevertheless be immersed, Without prior cooling, in the pene trant provided the temperature of the penetrant is not raised thereby above 30 C.

The fluorescent liquid penetrant employed may, for eX- ample, be any of those marketed under the trade names Zyglo Pentrex, Zyglo Super Pentrex, and Britemore.

The blade is submerged in the penetrant for a period of at least 30 seconds and preferably of 25 minutes, so as to ensure that the penetrant enters all the flaws in the article, after which surplus penetrant is drained from the article for a period of at least 30 seconds and preferably of 2-5 minutes.

The penetrant is then removed from any surface to be tested in such a way that the penetrant will remain in the flaws and in the said surface but will be completely removed from the unflawed parts thereof. This is effected partly by means of a washing operation but mainly by means of employing finely divided particulate material.

The said washing operation may consist of hosing the blade with lukewarm water e.g. at 30-45 C. This water must not contain a wetting agent or a detergent. The Washing operation should only be of sufficient duration to remove the obvious liquid penetrant film on the surface of the blade.

In order to facilitate subsequent handling, the blade is then dried in a stream of air. Complete drying of the blade is, however, unnecessary.

The removal of the surplus penetrant by the finely divided particulate material may be effected either by blowing the material onto the blade or by tumbling the blade in the material.

In the former case, the blade is transferred to a blast cabinet where all the surfaces of the blade are blasted with finely divided plum stones of grit size No. 3. The blast pressure within the cabinet is maintained at between 5 and 10 pounds per square inch, the pressure chamber and circulating system of the blast cabinet being such that, during blasting at least pounds of the finely divided plum stones is in circulation. Ultra violet light is provided within the blast cabinet, blasting being carried out for a length of time just sufiicient to remove background fiuorescence from the blade. Dust is continuously removed from the blast cabinet since the presence of excessive dust may prevent fine surface defects in the blade from showing up.

Alternatively, if the surplus penetrant is removed by tumbling, the tumbling operation may comprise tumbling the blade in a tumbling machine for a period of 30-40 minutes, the tumbling machine containing a Water saturated aggregate. This aggregate is formed by adding clean cold water to a mass consisting of 50% by weight of finely divided plum stones (e.g. British Standard Mesh size 12) and 50% by weight of granite or aloxite tumbling chips. The water is added to the said mass until the aggregate so formed is saturated and any excess water is run off. Tumbling thus takes place in a kind of mud or slurry.

After the blasting or tumbling operation, any finely divided particulate material or aggregate adhering to the blade is removed by blowing air onto the blade or by a cold water wash, after which the blade is dipped in hot water and is dried.

The blasting or tumbling operation is carried out in such a way and the finely divided particulate material or aggregate employed is such that the surfaces of the blade are not pitted or otherwise damaged whilst at the same time substantially no material is removed from them.

The blade is then submerged for a period of 5l0 minutes in a powder which is adapted to absorb or adsorb the liquid penetrant. This powder (hereinafter for convenience referred to as developer powder) may consist of or comprise silica or talc.

Surplus developer powder is then removed by blowing dry compressed air, at a pressure not exceeding 25 lbs. per square inch, onto the blade or, alternatively, by knocking the surplus developer powder olf. For a period of at least 5 minutes and preferably of 20 minutes the blade is allowed to stand so that the developer powder The present invention, in providing for the removal of the surplus penetrant by finely divided particulate material, obviates the need to use expensive chemicals for this purpose.

Iclaim:

1. A method of detecting flaws in a liquid-impermeable surface of a body having a-high quality surface finish comprising applying to said surface a liquid penetrant to cause the latter to penetrate into the said flaws; employing finely divided particulate organic material to remove thepenetrant completely from the unilawed parts of said surface while leaving the penetrant in said flaws and while leaving said surface substantially unimpaired in quality and dimensions; and rendering visible the penetrant which has been left in the flaws.

2. A method of detecting flaws in a liquid-impermeable surface of a body comprising applying to said surface a liquid penetrant to cause the latter to penetrate into the said'fiaws; employing powdered fruit stones to remove the.

penetrant completely from-the unflawed parts of said surface while leaving the penetrant in said flaws and while leaving said surface substantially unimpaired in quality and dimensions; and rendering visible the penetrant which has been left in the flaws.

3. A method'of detecting flaws in a liquid-impermeable surface of a body comprising applying to said surface a liquid penetrant to cause the latter to penetrate into the said flaws; employing powdered nut shells to remove the penetrant completely from the unfiawed parts of said surface while leaving the penetr-ant in said flaws and while leaving said surface substantially unimpaired in qualityand dimensions; and rendering visible the penetrant which has been left in the flaws.

4. A' method of deteeting'flaws in a liquid-impermeable surface of a body comprising applying to said surface a liquid penetrant to cause the latter to penetrate'into the said flaws; blowing and circulating finely divided dry particulate organic material on to said surface to remove the penetrant completely from the unfiawed parts of said surface while leavingthe penetrant in said flaws and while leaving said surface substantially unimpaired in quality and dimensions; continuously removing dust from said material duringiitsa circulationyand rendering visible the penetranttwhich' has been leftiin the flaws.

5. A method of detecting flaws in a liquid-impermeable surface of a body comprising applying to said surface a liquid penetrant to cause the latter to penetrate into the said-flaws; tumbling the body in a water-saturated aggregate comprising tfinely divided particulate material to remove thepenetrantcompletely from the unllawed parts of said surface whilesleaving' the'penetra-nt in said flaws; and rendering visible the penetrant which has been left in the flaws.- i

6. A method as claimed in claim in which said aggregate comprises tumbling chips.

7. A method as claimed in claim 5 in which said aggregate comprisessubstantially 50% by weight of finely divided plum stones and 50% by weight of tumbling chips formed from materials selected from-the group comprising granite and aloxite.

8. A method of detecting flaws in a liquid-impermeable 5 surface of a body comprising applying to said surface a liquid penetrantv to cause the latter to penetrate into the said flaws; employing finely divided particulate organic mate-rial to remove the penetran-t completely from the unflawed parts of said surface while leaving the penetrant in said flaws and while leaving said surface substantially unimpaired in quality and dimensions; and applying to said surface a penetrant-absorbent powder which renders visible the penetrant which has been left in the flaws. 9. A method of detecting flaws in a liquid-impermeable surface of a body comprising applying to said surface a fluorescent liquid penetrant to cause the latter to penett-rate into the said flaws; employing finely divided particulate organic material to remove the pen'etrant completely from the un l'lawed parts of said surface while leaving the penetrant in said'flaws andwhile leaving said surface substantially unimpaired in quality and dimensions; and employing ultra-violet light to render visible the penetrant which has been left in the flaws. 2 10. A method of detecting flawsina liquid-impermeable surface of a body comprising applying to said surface a liquid penetrant to cause the'latter to penetrate into the said flaws, the colour of said penetrant being readily distinguishable from that of the surface of the body; employing finely divided particulate organic material to remove the penetrant completely from the unflawed parts of said surface while leaving the penetran't in said flaws and while leaving said surface substantially unimpaired in quality and dimensions;iand rendering visible the penetrant which has been left in the flaws.

l l. A method as claimed in claim 10 in which the penetrant contains a non-fluorescent dye.

12.. A method of detecting flaws in a liquid-impermeable surface of a body comprising applying to said surface a liquid penetran-t to cause the latter to penetrate into the said' flaws; washing said surface and thereafter employing finely divided dry particulate organic material to remove the penetrant completely from the unfiawed' parts of said surface while leaving the penetrant in said flaws and while leaving said surface substantially uni-Inpaired in quality and dimensions; and rendering visible the penetrant which has been left in the flaws.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Catlin: Fluorescent Method Detects Leaks in Process Vessels, Chemical and Metallurgical Engineering, August 1943, page 11 6.

Ellis: Fluorescent Penetrant Inspection, Steel, Oct. 16, 1944, pp. 100-102. 

1. A METHOD OF DETECTING FLAWS IN A LIQUID-IMPERMEABLE SURFACE OF A BODY HAVING A HIGH QUALITY SURFACE FINISH COMPRISING APPLYING TO SAID SURFACE A LIQUID PENETRANT TO CAUSE THE LATTER TO PENETRATE INTO THE SAID FLAWS; EMPLOYING FINELY DIVIDED PARTICULATE ORGANIC MATERIAL TO REMOVE THE PENETRANT COMPLETELY FROM THE UNFLAWED PARTS OF SAID SURFACE WHILE LEANING THE PENETRANT IN SAID FLAWS AND WHILE LEAVING SAID SURFACE SUBSTANTIALLY UNIMPAIRED IN QUALITY AND DIMENSIONS; AND RENDERING VISIBLE THE PENETRANT WHICH HAS BEEN LEFT IN THE FLAWS. 